C language – One, Two, Multi dimensional Arrays in C

Feature of an array in C language

• An array is a derived data type. It is used to represent a collection of elements of the same data type.
• The elements can be accessed with the base address(index) and the subscripts define the position of the element.
• In an array, the elements are stored in the continuous memory location. The starting memory location is represented by the array name and it is known as the base address of the array.
• It is easier to refer to the array elements by simply incrementing the value of the subscript.

Array Initialisation

The values can be initialized to an array when they are declared like ordinary variables, otherwise, they hold garbage values.

The array can be initialized in two ways

• At compile time
• At run time

At compile time

Syntax: data_type array_name[size] = {List of values};

Description: the list of values must be separated by commas.

Example: int marks[3] = {70, 80, 90};

This statement declares the variable marks as an array of 3 elements and will be assigned to values specified in the list.

Like ordinary variables, the values to the array can be initialized as

marks[0] = 70;

marks[1] = 80;

marks[2] = 90;

These elements can be used like ordinary variables. Character array can also be initialized in a similar fashion.

Example:

char name[] = {'M','S','T'};

The above statement declares the name as an array of characters initialized with the string ‘MST’.

At Run time

The array can be explicitly initialized at run time.

Example:

while(i<=13)
{
   if(i<7)
      sum[i] = 0;
   else
      sum[i] = sum[i] + i;
}

Explanation: The while loop checks the condition i<=13. If condition is true then if statement checks the condition i<7, if condition is true then sum[i] the assigned to zero sum[i] assigned as sum[i]+i.

Like, the array can also be initialized by reading data items from the input.

Example:

int n[2];
scanf("%d%d", &n[0], &n[1]);

Here array n is declared as integer type variable, n[0], n[1] it reads through the scanf() function.

We can assign initial values to the elements of an array just as you can assign initial values to variables when they are declared.

This is done by simply listing the initial values of the array, starting from the first elements.

Values in the list are separated by commas and the entire list is enclosed in a pair of braces.

The statement int A[5] = {0, 0, 0, 0, 0}; declares an array called A to contain five integer values and initializes each of these elements to Zero. In a similar fashion, the statement int B[5] = {1, 2, 3, 4, 5} sets the value of B[0] to 1, B[1] to 2, B[2] to 3, and so on.

Arrays of characters are initialized in a similar manner; thus the statement char characters[5] = {‘a’, ‘b’, ‘c’, ‘d’, ‘e’}; defines the character array letters and initializes the five elements to the characters ‘a’, ‘b’, ‘c’, ‘d’, and ‘e’ respectively.

It is not necessary to completely initialize an entire array. If fewer initial values are specified, only an equal number of elements are initialized.

The remaining values in the array are set to zero.

Example:

float data[100] = {10, 20, 30};

The above initializes the first three values of data to 10, 20, and  30, and sets the remaining 97 elements to zero.

Example: Initializing Arrays

#include<stdio.h> 
int main (void)
{
  int values[10] = {1, 2, 3, 4,5};
  int i;
  for (i=5;i<10;++i)
    values[i] = i *i;
  for (i=0;i<10;++i)
  printf("array values[%i] = %i\n", i, values[i]);
return 0;
}

Entering data into the array

The data can be entered into an array using the input statement as well as loop statements.

Example program

Program to accept 5 numbers and print whether the number is even or odd.

/* Program to print whether the number is odd or even */
#include <stdio.h>
#include <conio.h>
int main()
{
  /* Local definitions */
  int a[5], i;
  for(i=0;i<5;i++)
  {
    printf("Enter the %d number : ", i+1);
    scanf("%d", &a[i]);
  }   /* for */
  for(i=0;i<5;i++)
  {
    if(a[i]%2==0)
    printf("%d Number is even. \n", a[i]);
    else
    printf("%d Number is odd. \n", a[i]);
  }  /*  for  */
  getch();
}  /*  main  */

Explanation: This program reads 5 integers into an array, then array values one by one and evaluates whether the number is even or odd number and prints them.

Example program in c language

Program to sort the given strings alphabetically

/* Program to sort the given strings alphabetically */
#include <stdio.h>
#include <string.h>
#include <conio.h>
int main()
{
  int i, j;
  char b[20];
  printf("Enter the text to sort :");
  gets(b);
  printf("Sorted Text are :");
  for(i=65;i<=90;i++)
  {
    for(j=0;j<=30;j++)
    {
       if (b[j] == toupper(i) || b[j] == tolower(i))
       printf("%c", b[j]);
    }   /* for  */
  }  /* for */
  getch();
}  /* main function */

Output
Enter the text to sort : I learn C Programming Language
Sorted Text are : aaaaCeeggggIilLmmnnnoPrrru

Explanation: The above program gets the string characters from the keyboard. ASCII equivalent of alphabets is used to sort out the given string.

The toupper() and tolower() string functions in if statement used to ignore priority of characters i.e., capital or small letters are treated the same. If the character value given by for loop i and string b[ ] value denoted by for loop j is same that value gets printed.

Because the value of a character supplied by the outer for loop is taken alphabetically.

Two-dimensional array in c language

In the C programming language, Two-dimensional arrays are used in a situation where a table of values needs to be stored in an array.

These can be defined in the same fashion as in one-dimensional arrays, except a separate pair of square brackets is required for each subscript.

Two pairs of square brackets are required for a two-dimensional array and three pairs are required for three-dimensional arrays and so on.

Syntax: data_type  – array_name[row size][column size];

Description: data_type – Specifies the type of data that will be contained in the array.

array_name  –  specifies the name of the array.

[row size]  –  specifies the name of the row.

[column size]  –  specifies the size of the column.

Example: int a[3][3];

Two-dimensional arrays are stored in a row-column matrix, where the left index indicates the row and the right indicates the column.

Example:

 int a[3][3];

Where ‘a‘ is the array name and it reserves 3 rows and 3 columns of memory.

The individual elements are identified by the index or subscript of an array from the above table example.

Example program

Program to specify the two-dimension array

/* Program using two dimension array */
#include <stdio.h>
void main()
{
   /* Local definitions */
   int stud[4][2]; /* An array name with 4 rows and 2 columns */
   int i;
   /* Statements */
   for(i=0;i<=3;i++)
   {
      printf("\n Enter the %d Student roll no and Mark:", i);
      scanf("%d%d", &stud[i][0], &stud[i][1]);
   }  /* for */
   for(i=0;i<=3;i++)
   printf("%d Students roll no %d mark %d", i, stud[i][0], stud[i][1]);
}   /* main */

Output
Enter the 0 student roll no and Mark: 7865 87
Enter the 1 student roll no and Mark: 8796 90
Enter the 2 student roll no and Mark: 2343 56
Enter the 3 student roll no and Mark: 6754 79
0 Students roll no 7865 mark 87
1 Students roll no 8796 mark 90
2 Students roll no 2343 mark 56
3 Students roll no 6754 mark 79

Explanation: Look at the scanf() statement used in the first for loop in the above example. In stud[i][1] and stud [i][1] the first subscript of the variable stud is row number which changes for every student.

Now that all data is stored in a continuous location. The second subscript tells the column number. The following diagram shows how the data is stored in the memory.

i.e., 7865 is stored in stud [0][0], 87 is stored in stud [0][1] and so on.

In fact, a two-dimensional array is nothing but a collection of a number of one-dimensional arrays placed one below the other.

Initializing a two-dimensional array

Like one dimensional array, the values can be initialized to the two-dimensional arrays at the time of declaration.

Syntax: data_type array_name[row_size][column_size] = {List of values};

Description : {List of variables} specifies the list of elements.

Example:

int stud [4][2] =
{
   {7865, 87},
   {8796, 90},
   {2443, 56}
   {6754, 79}
};

Remember that while initializing an array it is necessary to mention the second dimension, whereas the first dimension is optional. So the following will never work.

int arr[2] [ ] = {1, 2, 3, 4, 5, 6};

int arr[ ] [ ] = {1, 2, 3, 4, 5, 6};

We must mention the column size then only the compiler knows where the first row ends. The two sizes are optional if we initialize the array in the declaration part itself.

Example program

Program to illustrate Matrix Multiplication

/* Program for matrix multiplication */
#include <stdio.h>
int main()
{
   int a[5][5], b[5][5], c[5][5],r1 ,r2, c1, c2, i, j, k;
Step1:
   printf("\nEnter the size of the matrix A....");
   scanf("%d%d", &r1, &c1);
   printf("\nEnter the size of the matrix B....");
   scanf("%d%d", &r2, &c2);
   if(c1 == c2)
     goto step2;
   else
     printf("\nMultiplication is not possible");
      goto step1;
Step2:
   printf("\nEnter matrix A elements...\n");
   for(i=0;i<r1;i++)
   {
      for(j=0;j<c1;j++)
      scanf("%d", &a[i][j]);
   }
   printf("\nEnter matrix B elements...\n");
   for(i=0;i<r2;i++)
   {
      for(j=0;j<c2;j++)
      scanf("%d", &b[i][j]);
   }  /* for */
   for(i=0;i<r1;i++)
   {
      for(j=0;j<c1;j++)
      {
         c[i][j] = 0;
            for(k=0;k<c1;k++)
         c[i][j] = c[i][j] + a[i][k] * b[k][j];
      }  /* for */
   }  /* for */
   printf("\nThe resultant matrix is ....\n");
   for(i=0;i<r1;j++)
   {
      for(j=0;j<c1;j++)
      printf("%d\t", c[i][j]);
      printf("\n");
   }  /* for */
}  /*  main */

Output:

Enter the size of the matrix A....3 3
Enter the size of the matrix B....2 2
Mulplication is not possible
Enter the size of the matrix A....3 3
Enter the size of the matrix B....3 3
Enter matrix A elements...
 2 2 2 2 2 2 2 2 2 
Enter matrix B elemrnts...
 3 3 3 3 3 3 3 3 3 
The resultant matrix is ....
18    18    18
18    18    18
18    18    18
....

Explanation: The program reads the size of the matrix, then checks rows and columns are equal or not.

If rows and columns are equal further execution starts, else it prints multiplication is not possible. The i and j for loop are used to get both A and B matrices.

The other i and j for loop are used to calculate the matrix multiplication and the final i and j for loop are used to print the resultant matrix.

Multi-dimensional array in c language

Similarly, like one and two-dimensional arrays, the C language allows multi-dimensional arrays.

The dimension with three or more is called multi-dimensional arrays.

Syntax: data_type  array_name[size1][size2]……[size n];

Description:

datatype is the type of data, that will be stored in an array.

array_name  is the name of the array.

size1, size2…sizen are the sizes of the dimensions or subscripts.

Example:

   int a[3][3][3];

   float table, b[4][4][4][4];

here,

a  is the three-dimensional array declared as an integer type and can hold 27 elements.

 b  is the four-dimensional array declared as float type and can hold 256 elements.

The array of more than three dimensions is not used often. Multi-dimensional arrays are slower than the single dimension in execution.